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Direct Observation of Reversible and Irreversible Stomatal Responses of Attached Sunflower Leaves to SO₂

The National Institute for Environmental Studies, Yatabe, Tsukuba, Ibaraki, 305, Japan, Department of Agricultural Engineering, Ehime University, Matsuyama 790, Japan, Botany Department, Duke University, Durham, North Carolina 27706

The effects of SO₂ on stomatal aperture of attached sunflower leaves were observed with a remote-control light microscope system that permitted continuous observation of stomatal responses over periods of several hours. The relationship between actual stomatal aperture and stomatal conductance, measured with a porometer, also was examined on leaves before and after exposure to SO₂.

A distinction between uninjured and injured regions was clearly visible on leaves after exposure to 1.5 microliters per liter SO₂ for less than an hour. During the exposure, the mean value of apertures for many stomata, which indicates stomatal conductance and transpiration rate, tended to decrease simultaneously in the uninjured and injured regions. However, the rate of decrease in the injured region was slower than that in the uninjured region because of a transient opening induced by water-soaking in the injured region. The transient opening was less common in stomata near veins and veinlets.

There was a good correlation between pore width and stomatal conductance measured with a porometer before exposure to SO₂. This correlation continued in leaves exposed to SO₂ until visible, irreversible injury occurred, but then it disappeared.

The results of these experiments indicate the necessity of continuous observation of individual stomata under the microscope to understand the effects of air pollutants such as SO₂ on stomatal behavior.

This article has been cited by other articles:

				K. Omasa and K. Takayama Simultaneous Measurement of Stomatal Conductance, Non-photochemical Quenching, and Photochemical Yield of Photosystem II in Intact Leaves by Thermal and Chlorophyll Fluorescence Imaging Plant Cell Physiol., December 15, 2003; 44(12): 1290 - 1300. [Abstract] [Full Text] [PDF]

				J. L. Croxdale Stomatal patterning in angiosperms Am. J. Botany, August 1, 2000; 87(8): 1069 - 1080. [Abstract] [Full Text]